TECHNICAL FIELD
[0001] The present disclosure relates to a controller apparatus and a control method for
an electric power tool including, for example, a DC brushless motor, and an electric
power tool.
BACKGROUND ART
[0002] In recent years, DC brushless motors are often used in electric power tools. As compared
to conventional DC motors, this DC brushless motor does not require brush replacement,
and has a long service life. However, the motor uses a switching device instead of
a brush, and it is necessary to protect both the battery and the switching device
from large current that flows when the motor is locked, upon overloaded, or the like.
[0003] As an example of a technique for solving the problem, Patent Document 1 proposes
a method in which two filters having different cutoff frequencies are provided in
one current detection circuit to protect both a battery (average current) and a switching
device (instantaneous current).
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0004]
[Patent Document 1] Japanese Patent Publication No. 5814065
[Patent Document 2] Japanese Patent Laid-open Publication No. H04-368490
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] However, with the method of Patent Document 1, even if the overcurrent protection
of the battery and the switching device can be performed, controllability of the electric
power tool itself is not improved. In addition, from the viewpoint of continuity of
use of the electric power tool, it is important to control the electric power tool
not to lead to the overcurrent at the stage before detecting the overcurrent.
[0006] An object of the present disclosure is to solve the above-described problems, and
to provide a controller apparatus and a control method for an electric power tool,
each capable of controlling the electric power tool not to lead to any overcurrent
at the stage before detecting the overcurrent, and to provide an electric power tool
including the controller apparatus.
MEANS FOR DISSOVING THE PROBLEMS
[0007] According to the first aspect of the disclosure, there is provided a controller apparatus
for an electric power tool including a battery and a DC brushless motor. The controller
apparatus includes a current detector that detects an instantaneous current flowing
in the DC brushless motor; a current calculator that calculates one of an average
value and an effective value of the instantaneous current detected by the current
detector; a current controller configured to utilize a result from the current calculator
as a detected value; and a speed controller configured to generate a target value
of the current controller, The controller apparatus further includes a limiter that
limits the target value of the current controller, the limiter being provided at an
output stage of the speed controller.
[0008] According to the second aspect of the disclosure, there is provided a control method
for an electric power tool including a battery and a DC brushless motor. The control
method includes: a current detection step of detecting an instantaneous current flowing
in the DC brushless motor; a current calculation step of calculating one of an average
value and an effective value of the instantaneous current detected in the current
detection step; a current control step of utilizing a result from the current calculation
step as a detected value; a speed control step of generating a target value in the
current control step; and a step of limiting the target value in the current control
step by a limiter provided at an output stage in the speed control step.
[0009] According to the third aspect of the disclosure, there is provided an electric power
tool including a battery and a DC brushless motor. The electric power tool includes
the above-mentioned controller apparatus for the electric power tool.
EFFECT OF THE INVENTION
[0010] According to the controller apparatus, the control method, and the like of the present
disclosure, the single current detector can protect the overcurrent of the battery,
the switching devices, and the circuits. Since the limiter of current control operates
before the overcurrent protection is activated, the overcurrent can be prevented in
advance. In addition to that, by inserting the current controller into a minor loop
of the speed controller, the control performance of the entire electric power tool
can be improved, and control that does not lead to any overcurrent can be done before
the overcurrent is detected.
BRIEF DESCRIPTION OF THE DRAWING
[0011] Fig. 1 is a block diagram illustrating a configuration example of an electric power
tool according to an embodiment of the present disclosure.
MODE FOR CARRYING OUT THE INVENTION
[0012] Fig. 1 is a block diagram illustrating a configuration example of an electric power
tool according to an embodiment of the present disclosure. Referring to Fig. 1, the
electric power tool according to the embodiment includes, for example, a DC brushless
motor (hereinafter, referred to as a motor) 1, a PWM inverter circuit 2, a gear 3,
a chuck 4, a rechargeable battery 5, a capacitor 6, a current detection resistor 7,
and a motor controller apparatus 10. In this case, the motor controller apparatus
10 includes a current detector 11, a current calculator 12, an overcurrent detector
51, a speed controller 52, a current controller 53, and a gate controller 20.
[0013] The motor controller apparatus 10 according to the present embodiment protects the
switching devices, the circuits, and a battery by detecting the instantaneous current
and the average current of the current supplied to the PWM inverter circuit 2. At
the same time, the motor controller apparatus 10 prevents the overcurrent in advance
by controlling the detected average current and providing a current limiter 24 that
limits a target value at an output stage of the speed controller 52 that is a current
controller. In addition, the speed controller 52 is provided in front of the current
controller 53, and the current control is done by a minor loop for the speed control,
so that the speed sensitivity and the stability of speed control of the electric power
tool are improved.
[0014] Referring to Fig. 1, a DC voltage from the rechargeable battery 5 is supplied to
the PWM inverter circuit 2 via the capacitor 6 and the current detection resistor
7. The PWM inverter circuit 2 modulates the supplied DC voltage in accordance with
six gate drive signals G1 to G6 from the gate controller 20, converts a modulated
DC voltage to an AC voltage, and outputs the AC voltage to the motor 1. In this case,
the rotation of the motor 1 is transmitted to the chuck 4 of the electric power tool
via the gear 3. Based on motor rotational position signals from Hall elements 41 to
43 provided in the motor 1, a PWM signal from the current controller 53, and a gate
block signal from the overcurrent detector 51, then the gate controller 20 generates
a speed detected value and the gate drive signals G1 to G6.
[0015] The voltage detected by the current detection resistor 7 is outputted to the current
detector 11, and the current detector 11 converts the voltage into a corresponding
current value, and then, outputs the current value to a non-inverting input terminal
of a comparator 13 and the current calculator 12. In the current calculator 12, for
example, the current value is added for a predetermined time interval using an adder,
and an average value is calculated and outputted to a subtractor 25. It is noted that
the current calculator 12 may calculate an effective current value or the like for
a predetermined time interval, instead of the average current value for the predetermined
time interval.
[0016] The overcurrent detector 51 includes the comparator 13 and a maximum current signal
generator 14. The comparator 13 compares an instantaneous current signal from the
current detector 11 with a maximum current signal indicating the maximum current value
from the maximum current signal generator 14, generates a gate block signal from a
result of the comparison, and outputs the gate block signal to the gate controller
20. When the instantaneous current exceeds the maximum current value, the gate controller
20 immediately stops drive of the PWM inverter circuit 2 and protects the switching
devices.
[0017] The speed controller 52 includes an absolute value calculator 30, a target speed
value generator 21, a subtractor 22, a PI controller 23 that performs proportional-integral
control on motor speed, and the current limiter 24. The absolute value calculator
30 calculates an absolute value of the speed detected value from the gate controller
20, and outputs a calculated absolute value of the speed detected value to the subtractor
22. The subtractor 22 subtracts the absolute value of the speed detected value from
a target speed value from the target speed value generator 21, and outputs a result
of the subtraction to the PI controller 23. The PI controller 23 performs proportional-integral
control on the motor speed based on the input subtraction result, and outputs a target
current value for the control to the subtractor 25 via the current limiter 24. In
this case, the current limiter 24 prevents the overcurrent in advance, and protects
the circuits and the battery by limiting the target current value corresponding to
the target speed value within a predetermined value.
[0018] The current controller 53 includes the subtractor 25, a PI controller 26, a limiter
27, a comparator 28, and a triangular wave generator 29. The subtractor 25 subtracts
an average current signal from the current calculator 12 from a target current value
signal indicating the target current value, so that a current control value signal
indicating a result of the subtraction is outputted to the PI controller 26. The PI
controller 26 performs proportional-integral control on the current control value,
and outputs a control signal to a non-inverting input terminal of the comparator 28
via the limiter 27. In this case, the limiter 27 controls an amplitude value of the
PWM signal outputted from the comparator 28 within a predetermined value. The comparator
28 generates a PWM signal for driving the motor 1 by PWM modulation, and outputs the
PWM signal to the gate controller 20 by comparing the control signal from the limiter
27 with a triangular wave from the triangular wave generator 29.
[0019] The gate controller 20 controls the operation of the PWM inverter circuit 2 by generating
the six gate drive signals G1 to G6 based on the PWM signal and the gate block signal
and outputting the gate drive signals G1 to G6 to the PWM inverter circuit 2.
[0020] In the controller apparatus 10 for the electric power tool according to the embodiment
configured as described above, the single current detector 11 enables the overcurrent
protection of the switching devices and the circuits in the PWM inverter circuit 2
and the battery 5. In addition, since the current limiter 24 of the current control
operates before overcurrent protection can be activated, the overcurrent can be prevented
in advance. In addition to that, the target current value is given from the speed
controller 52 to the current controller 53 that generates the PWM signal to form the
minor loop of the speed controller 52, so that there is such an effect that the control
performance of the electric power tool itself can be achieved.
[0021] In the above embodiment, for example, a rotary electric power tool of a drill driver
has been described. However, the present disclosure is not limited to this, and the
present disclosure can be applied to an impact type electric power tool.
[0022] In the above embodiment, the rechargeable battery 5 that is a secondary battery is
provided. However, the present disclosure is not limited to this, and other types
of batteries such as a primary battery may be used.
[0023] In the above embodiment, the motor controller apparatus 10 may be configured mainly
of hardware, or may be configured mainly of software.
DESCRIPTION OF REFERENCE CHARACTERS
[0024]
1: MOTOR
2: PWM INVERTER CIRCUIT
3: GEAR
4: CHUCK
5: RECHARGEABLE BATTERY
6: CAPACITOR
7: CURRENT DETECTION RESISTOR
10: MOTOR CONTROLLER APPARATUS
11: CURRENT DETECTOR
12: CURRENT CALCULATOR
13: COMPARATOR
14: MAXIMUM CURRENT SIGNAL GENERATOR
20: GATE CONTROLLER
21: TARGET SPEED VALUE GENERATOR
22: SUBTRACTOR
23: PI CONTROLLER
24: CURRENT LIMITER
25: SUBTRACTOR
26: PI CONTROLLER
27: LIMITER
28: COMPARATOR
29: TRIANGULAR WAVE GENERATOR
30: ABSOLUTE VALUE CALCULATOR
41 to 43: HALL ELEMENT
51: OVERCURRENT DETECTOR
52: SPEED CONTROLLER
53: CURRENT CONTROLLER
1. A controller apparatus for an electric power tool comprising a battery and a DC brushless
motor, the controller apparatus comprising:
a current detector that detects an instantaneous current flowing in the DC brushless
motor;
a current calculator that calculates one of an average value and an effective value
of the instantaneous current detected by the current detector;
a current controller configured to utilize a result from the current calculator as
a detected value; and
a speed controller configured to generate a target value of the current controller,
wherein the controller apparatus further comprises a limiter that limits the target
value of the current controller, the limiter being provided at an output stage of
the speed controller.
2. A control method for an electric power tool comprising a battery and a DC brushless
motor, the control method comprising:
a current detection step of detecting an instantaneous current flowing in the DC brushless
motor;
a current calculation step of calculating one of an average value and an effective
value of the instantaneous current detected in the current detection step;
a current control step of utilizing a result from the current calculation step as
a detected value;
a speed control step of generating a target value in the current control step; and
a step of limiting the target value in the current control step by a limiter provided
at an output stage in the speed control step.
3. An electric power tool including a battery and a DC brushless motor, the electric
power tool comprising a controller apparatus for the electric power tool as claimed
in claim 1.